turbopixel :
First, list exactly what you have, your motherboard, cpu, psu. And look after the ampere on the sticker of your psu, at 12v combined power or so. The 12v rail is important, because graphics card and cpu are taking its power from there. If your psu don't have a power connector, then you can use low power graphics card. Non overclocked Nvidia GTX 750 Ti could be a good boost for your system. But it depends on the other parts. Probably it can't be used its full power, as other parts could hinder it. Then it would be wise to take a lower level card.
I have a Medion Akoya E4005 E (MD 8357)
Processor: amd a10 7800 Quad Core with intergrated R7 Series Graphics (3,5 ghz up to 3,9 ghz)
RAM: 8 GB (I upgraded it)
PSU: max 336W
Internal Hard Drive: 1TB
Windows 8.1 (I will upgrade it to windows 10)
I don't know what motherboard I have but it has a 14 pin connecter
the sticker on the PSU says:
AC INPUT 230-240V-,4A,50-60Hz
DC OUTPUT +12V1 +12V2 +5Vsb -12V
_________ 16.0A 16.0A 2.5A 0.3A
I also saw a connecter for the motherbord from 24 pin to 14 pin but it's for the Lenovo. Does this connecter work for my pc as well?